The present invention relates to an internal combustion engine gas flow rate control system and, more particularly, to a gas flow rate control system for controlling the recirculation of gas discharge from the engine back to the same engine in accordance with engine operating conditions and also in accordance with flow rate adjustments made to the gas flow rate control system.
A crankcase ventilation system is a way for gases to escape in a controlled manner from the crankcase of an internal combustion engine. A common type of such system is a positive crankcase ventilation (PCV) system. The heart of this system is a PCV valve—a single channel variable-restriction valve that can react to changing pressure values and intermittently vary flow rates while allowing the passage of the gases to their intended destination. In most modern vehicles the intended destination is the engine's intake stream.
Internal combustion inevitably involves a small but continual amount of blow-by gases, which will occur when some of the gases from the combustion leak past the piston rings to end up inside the crankcase. The gases could be vented through a simple hole or tube directly to the atmosphere, or they could “find their own way out” past baffles or past the oil seals of shafts or the gaskets of bolted joints. This is not a problem from a mechanical engineering viewpoint alone; but from other viewpoints, such as cleanliness for the user and environmental protection, such simple ventilation methods are not enough; escape of oil and gases must be prevented via a closed system that routes the escaping gases to the engine's intake stream and allows fresh air to be introduced into the crankcase for better and more efficient combustion.
From late in the 19th century through the early 20th century, blow-by gases were allowed to find their own way out past seals and gaskets in automotive vehicles. It was considered normal for oil to be found both inside and outside an engine, and for oil to drip to the ground in small but constant amounts. This was also true for steam engines and steam locomotives in the decades before. Bearing and valve designs generally made little to no provision for keeping oil or waste gases contained. Sealed bearings and valve covers were only for special applications. For example, oilers kept the locomotives and rolling stock of railroads continually supplied with oil both inside and out. Although it was applied sparingly to oil cups and oil holes, it was not expected to stay hermetically sealed off from dripping and leaking to the wider environment. At the time, gaskets and shaft seals were meant only to limit loss of oil and were usually not expected to entirely prevent it. In internal combustion engines, the hydrocarbon-rich blow-by gases would diffuse through the oil in the seals and gaskets into the atmosphere. Engines with high amounts of blow-by (e.g., worn out ones, or ones not well built to begin with) would leak profusely.
From 1928 until the early 1960s, car and truck gasoline operated internal combustion engines vented combustion gases directly to the atmosphere through a simple vent tube. Frequently, this consisted of a pipe (the ‘road draft tube’) that extended out from the crankcase down to the bottom of the engine compartment. The bottom of the pipe was open to the atmosphere, and was placed such that when the car was in motion a slight vacuum was obtained, helping to extract combustion gases as they collected in the crankcase. The vacuum was satisfied by a vent, typically in the valve or valley cover, creating a constant flow of clean air through the engine's air volume. The oil mist would also be discharged, resulting in an oily film being deposited in the middle of each travel lane on heavily-used roads. The system was not positive though, as gases could travel both ways, or not move at all, depending on conditions.
During the World War II years, a different manner of crankcase ventilation had to be invented to allow tank engines to operate during deep fording operations where the normal draft tube ventilator would have allowed water to enter the crankcase and destroy the engine. The PCV system and its control valve were invented to meet this need, but a need for this system on automobiles was not recognized.
In 1952, a professor at the California Institute of Technology, postulated that unburned hydrocarbons were a primary constituent of smog, and that gasoline powered automobiles were a major source of those hydrocarbons. After further investigation by the GM Research Laboratory, it was discovered that the road draft tube was a major source of the hydrocarbons coming from the automobile. GM's Cadillac Division, which had built many tanks during World War II, recognized that the PCV valve could be used to become the first major reduction in automotive hydrocarbon emissions. After confirming the PCV valves' effectiveness at hydrocarbon reduction, GM offered the PCV solution to the entire U.S. automobile industry, royalty free, through its trade association, the Automobile Manufacturers Association (AMA). In the absence of any legislated requirement, the AMA members agreed to put it on all California cars voluntarily beginning in 1961, with national application following one year later.
The PCV valve is only one part of the positive crankcase ventilation system, which is essentially a variable and calibrated air leak, whereby the engine returns its crankcase combustion gases. Instead of the gases being vented to the atmosphere, these gases are fed back into the intake manifold, re-entering the combustion chamber as part of a fresh charge of air and fuel. All the air collected by the air cleaner (and metered by the mass flow sensor, on a fuel injected engine) goes through the intake manifold. The PCV system just diverts a small percentage of this air via the breather to the crankcase before allowing it to be drawn back into the intake tract again. The positive crankcase ventilation system is an “open system” in that fresh exterior air is continuously used to flush contaminants from the crankcase and into the combustion chamber.
The system relies on the fact that, while the engine is running under light load and moderate throttle opening, the intake manifold's pressure is always less than crankcase pressure. The lower pressure of the intake manifold draws gases towards it, pulling air from the breather through the crankcase where the air is diluted and mixed with combustion gases through the PCV valve, and returned to the intake manifold.
The positive crankcase ventilation system usually consists of the breather tube and the PCV valve. The breather tube connects the crankcase to a clean source of fresh air—the air cleaner body. Usually, clean air from the air cleaner flows into this tube and into the engine after passing through a screen, baffle, or other simple system to arrest a flame front in order to prevent a potentially explosive atmosphere within the engine crankcase from being ignited from a backfire into the intake manifold. The baffle, filter, or screen also traps oil mist, and keeps it inside the engine. Once inside the engine, the air circulates around the interior of the engine, picking up and clearing away combustion byproduct gases, including any substantive amounts of water vapor which includes dissolved chemical combustion byproducts. The combined gases then exit through another simple baffle, screen, or mesh to trap oil droplets before being drawn out through the PCV valve and into the intake manifold.
The PCV valve connects the crankcase to the intake manifold from a location on the internal combustion engine more-or-less opposite the breather connection. Typical locations include the opposite side valve cover that the breather tube connects to on a V-shaped engine block. A typical location for the PCV valve is on a valve cover, although some engines place the valve in locations far from the valve cover.
The valve is simple, but actually performs a complicated control function. An internal restrictor (generally a cone or ball) is held in “normal” (engine off, zero vacuum) position with a light spring, exposing the full size of the PCV opening to the intake manifold. With the engine running, the tapered end of the cone is drawn towards the opening in the PCV valve by manifold vacuum, restricting the opening proportionate to the level of engine vacuum vs. spring force. At idle, the intake manifold vacuum is near maximum. It is at this time the least amount of blow by is actually occurring, so the PCV valve provides the largest amount of (but not complete) restriction. As engine load increases, vacuum on the valve decreases proportionally and blow by increases proportionally. With a lower level of vacuum, the spring returns the cone to the “open” position to allow more air flow. At full throttle, vacuum is much reduced, down to between 1.5 and 3 inches of Hg. At this point the PCV valve is nearly useless, and most combustion gases escape via the “breather tube” where they are then drawn into the engine's intake manifold. Should the intake manifold's pressure be higher than that of the crankcase (which can happen in a turbocharged engine, or under certain conditions of use, such as an intake backfire), the PCV valve closes to prevent reversal of the exhausted air back into the crankcase again.
It is critical that the parts of the PCV system be kept clean and open, otherwise air flow will be insufficient. A plugged or malfunctioning PCV system will eventually damage an engine. PCV problems are primarily due to neglect or poor maintenance, typically engine oil change intervals that are inadequate for the engine's driving conditions. A poorly-maintained engine's PCV system will eventually become contaminated with sludge, causing serious problems. If the engine's lubricating oil is changed with adequate frequency, the PCV system will remain clear practically for the life of the engine. However, since the valve is operating continuously as one operates the vehicle, it will fail over time. Typical maintenance schedules for gasoline engines include PCV valve replacement whenever the air filter or spark plugs are replaced. The long life of the valve despite the harsh operating environment is due to the trace amount of oil droplets suspended in the air that flows through the valve that keep it lubricated.
Most gasoline powered internal combustion engines still utilize PCV valves. The basic design of the PCV valve has not changed much in the more than 40 years since its first introduction on passenger vehicles. The existing single channel valve design works well on stock engines, but efficient operation still depends on system maintenance to prevent blockages.
The operating characteristics that define a PCV valve are: idle flow rate; cruise flow rate; and transition vacuum level. Idle flow rate is the determination of the quantity of gas flowing through the PCV valve during high vacuum conditions existing when an engine is idling. Cruise flow rate is the determination of the quantity of gas flowing through the PCV valve during low vacuum conditions when the engine is operating at higher rpm's during, for example, vehicle acceleration. Transition vacuum level is the vacuum level at which the PCV valve switches from a low to a high flow rate.
There are certain physical characteristics of stock PCV valves that can severely limit their utility. Usually, a given PCV valve is designed to operate efficiently with one specific engine type. The physical characteristics of the PCV valve are designed for proper operation of the engine type with which it is paired. The spring strength of the PCV valve is dictated to cause the PCV valve piston to operate between low and high flows depending upon the vacuum level that exists at the transition point. Internal flow rates of the PCV valve are dictated by the piston to body clearance and the taper of the piston in relation to the internal shape of the single channel body. Since PCV valves are manufactured and sold as sealed units, it is difficult, if not impossible, to determine the various specifications for the variety of PCV valves presently on the market.
High performance engines almost always have a non-standard engine combination for which a stock PCV valve will not operate efficiently, or not work at all. A mismatched valve can have an insufficient flow rate, in which case the crankcase will not be ventilated properly. Also a mismatched PCV valve may have an excessive flow rate, which may lead to engine tuning difficulties and possible spark plug fouling. If the vacuum profile of the high performance engine does not match the vacuum profile of the stock PCV valve, proper opening and closing functionality of the valve will also be lost or greatly reduced, which can lead to both inadequate or excessive flow rates and the related issues already discussed.
In some instances, stock PCV valves will not seal completely against reverse flow under positive pressure conditions, such as in supercharged or turbocharged applications. If the PCV valve does not seal properly, the crankcase can be positively pressurized causing damage to the engine. Lastly, in some extreme performance applications, the engine does not generate sufficient vacuum to close any type of PCV valve properly. In this case, a fixed orifice type valve is desired, whereby the vapors flow through a fixed flow restriction. Although stock type fixed orifice PCV valves do exist, they do not offer the ability for the user to alter the flow rate through the fixed flow restriction.
In order to overcome the stated deficiencies the present invention relies upon a dual channel or dual circuit PCV valve where each circuit is manually adjustable for greater response and efficiency. Standard PCV valves are designed to operate within the known parameters of a single engine type. These valves are not adjustable, but are rather sealed units preset for functioning by their internal design and operational parameters. As stated above, in high performance circumstances, or with non-standard engine operating parts, stock PCV valves will not properly function as intended and may cause more serious problems over time to engine efficiency and wear. The adjustable two circuit PCV valve allows for the appropriate adjustment of each circuit, high and low vacuum, to the operational characteristics of the engine.
It is, thus, one object of the present invention to provide two independent channels or circuits, one for idle (high vacuum) and one for cruise (low vacuum), in a PCV valve. It is also an object of the present invention to provide individual manual adjustment control over each of the high and low vacuum circuits, i.e., the idle and cruise circuits, to permit a more appropriate setting for operational response of the engine. It is a further object of the present invention to provide a better manual control over the baseline flow rate of the blow by gases and to more accurately set the vacuum level for transition from low to high flow through the PCV valve. It is a still further object of the present invention to provide a PCV valve which will seat against the reverse flow under positive pressure conditions, such as boost in a turbocharged or supercharged application. It is yet a further object of the present invention to provide an orifice between the two circuits to also control the amount of additional gas flow when the engine is in cruise mode.
Other objects will appear hereinafter.